(1) Field of the Invention
The present invention relates to a panel-type image display device and a liquid crystal television.
(2) Description of Related Art
Image signals input to panel-type image display devices, liquid crystal television s, and plasma televisions and so on are displayed on the screen after image qualities, such as contrast, white balance, brightness are adjusted in image quality control circuits. In addition, not only normal image signals but also on-screen display (OSD) signals that are superimposed onto the normal image signals are displayed on the TV screen. OSD signals are signals for a menu screen that are used for image quality adjustment and sound quality adjustment, signals that are used to display black masked portions, which appear when images with aspect ratio of 4 to 3 are displayed on screens for images with aspect ratio of 16 to 9, on both right and left sides of the TV screen, and signals that are used to display black masked portions, which appear when images with aspect ratio of 16 to 9 are displayed on screens for images with aspect ratio of 4 to 3, on both upper and lower sides of the TV screen and the like.
In Japanese Patent Laid-Open No. H10-079899, a television wherein on-screen display signals are adjusted so that on-screen displays are not adversely affected by image quality adjustments has been disclosed. In this patent reference, the adjustment of the on-screen display signals is performed in such a way as to compensate the influences of the image quality adjustments by use of an on-screen display control circuit.
In Japanese Patent Laid-Open No. 2005-026814, an image display device has been disclosed, wherein the existence of a side panel 16 to 9 image signal is detected; the brightness level of the side panel 16 to 9 image signal is detected; the brightness level of the image signal is obtained; and at the same time the image quality compensation according to the detected result of the brightness level of the side panel and the detected result of the brightness level of the image signal is performed.
In above-mentioned conventional panel-type image display devices, liquid crystal televisions, and plasma televisions, however, there is often the case where a processing block wherein OSD signals are superimposed onto image signals is followed by another block wherein image adjustments are performed. In this case, there are problems in that not only the image qualities of the normal image signals but also those of the superimposed OSD signals are adjusted with the result that colors of OSD displays are changed.
As to the technologies described in Japanese Patent Laid-Open No. H10-079899, there is a possibility that if the amount of image quality adjustment is large, the level of OSD signals is saturated when an image quality compensation is performed on OSD signals and as a result, the intended OSD displays cannot be obtained.